1. Field of the Invention
The present invention relates to a liquid jet head, and a liquid jet apparatus, such as a recording head for an ink jet recording apparatus, an electrode member ejection head for an electrode forming apparatus, an organic substance jet head for a bio chip manufacture apparatus, etc., in which liquid is ejected by deformation of piezoelectric elements formed on a surface of a diaphragm formed as a part of pressure generating chambers communicating with nozzle orifices from which liquid is ejected.
2. Description of Related Art
A typical inkjet recording head (a kind of liquid jet head) using a longitudinally oscillating piezoelectric transducer (referred to below as simply a “recording head”) has, as shown in FIG. 16, an ink path unit 1 in which a plurality of nozzle openings 8 and a pressure generation chamber 7 are formed, and a head case 2 to which this ink path unit 1 is bonded and in which piezoelectric transducers 6 are housed.
The ink path unit 1 is a laminar construction including a nozzle plate 3 in which the nozzle openings 8 are arranged in rows orthogonally to the recording medium surface, a flow channel substrate 4 in which a pressure generation chamber 7 is disposed communicating with each of the nozzle openings 8, and a diaphragm 5 covering the bottom opening of each pressure generation chamber 7. An ink reservoir 9 communicating with each pressure generation chamber 7 by way of ink supply path 10 and storing the ink supplied to each pressure generation chamber 7 is formed in the flow channel substrate 4. It should be noted that two sets of nozzle openings 8 and pressure generation chambers 7 arc shown in the example in FIG. 16.
The head case 2 is made from synthetic resin with the piezoelectric transducers 6 disposed in through-spaces 16, which are vertically oriented as seen in the figure. The spaces 16 extend in line with the rows of nozzle openings 8, and there are two spaces 16 corresponding to the rows of the nozzle openings 8. The back end side of each piezoelectric transducer 6 is bonded to a fixed plate 11 affixed to the head case 2, and the front end side of each piezoelectric transducer 6 is bonded to a pad 5C on the bottom surface of the diaphragm 5.
The piezoelectric transducers 6 are forced to expand and contract longitudinally by applying a drive signal generated by a drive circuit (not shown in the figure) to the transducers 6 by way of flexible printed circuit 13. Expansion and contraction of the piezoelectric transducers 6 cause the pad 5C of the diaphragm 5 to vibrate and thereby change the pressure inside the pressure generation chamber 7 so that ink inside the pressure generation chamber 7 is discharged from the nozzle opening 8 as an ink droplet. Also shown in FIG. 16 is the ink refilling tube 15 for refilling the ink reservoir 9 with ink from an ink cartridge (not shown in the figure).
The diaphragm 5 in this example is made from a polyphenylene sulfide (PPS) film, and a damper chamber 12 for absorbing through the diaphragm 5 pressure change in the ink reservoir 9 during ink discharge is formed in the head case 2 at an appropriate position to the ink reservoir 9. If this damper chamber 12 is an independent space that does not communicate with the exterior, air inside the damper chamber 12 can dissolve into the ink through the diaphragm 5 made of PPS film, thereby lowering the pressure inside the damper chamber 12, increasing the tension of the diaphragm 5, and can thus easily make it difficult to achieve the desired damping effect. This pressure drop inside the damper chamber 12 is therefore prevented by opening an external communication path 14 passing from the inside surface of the damper chamber 12 toward and out the back side of the head case 2 so that the damper chamber 12 can communicate with the outside.
A problem with the conventional recording head described above is that the damper chamber 12 is open to the air. When the recording head is left unused or stored for a long time, water in the ink within the ink reservoir 9 is able to pass as water vapor through the PPS film diaphragm 5 and the viscosity of ink inside the ink reservoir 9 gradually increases. The ink can even dry to the point that clogging of the flow path cannot be corrected and ink cannot be normally discharged even after a cleaning operation, for example, that forcibly vacuums ink from within the ink path when the recording head is used the next time. This tendency is particularly pronounced with pigment inks that easily increase in viscosity, and pigment inks are increasingly used in order to achieve a desired print quality.
There is therefore a strong need for an inkjet recording head whereby this increase in ink viscosity can be prevented during extended storage.
It is also desirable in achieving a means for solving this problem to minimize the number of parts and achieve high precision and quality with the simplest possible method.
The present invention is directed to solving these problems and an object of the invention is to provide an inkjet recording head and an inkjet recording apparatus capable of preventing an increase in ink viscosity inside the ink flow paths during long term storage.